Movie piracy is a cause of substantial revenue loss to the motion picture industry. Illegally copied movies, filmed during projection with video cameras or camcorders and similar devices, are a significant contributing factor to revenue loss. Even the questionable quality of movies pirated in this fashion does not prevent them from broad distribution in the “black market”, especially in some overseas markets, and on the Internet. As video cameras improve in imaging quality and become smaller and more capable, the threat of illegal copying activity becomes more menacing to motion picture providers. While it may not be possible to completely eliminate theft by copying, it can be advantageous to provide display delivery techniques that frustrate anyone who attempts to copy a motion picture using a portable video camera device. While this is a highly visible problem in the motion picture industry, this same problem is likely to be manifested in other industries that use digital media.
Skilled practitioners know how to provide a distinct symbol or watermark to an original still image as a means of image or copy identification, such as in order to authenticate a copy. U.S. Pat. No. 5,875,249 (Mintzer et al.), U.S. Pat. No. 6,031,914 (Tewfik et al.), and U.S. Pat. No. 5,912,972 (Barton) disclose methods of applying a perceptually invisible watermark to image data as verification of authorship or as evidence that an image has not been altered. Although, such methods identify and validate image data, they provide no direct means of protection against copying an image, for example, with a conventional scanner and color printer. In contrast, U.S. Pat. No. 5,530,759 (Braudaway et al.) discloses providing a visible, color correct watermark that is generated by altering brightness characteristics, but not chromaticity of specific pixels in the image. Yet the approach used in U.S. Pat. No. 5,530,759 could be objectionable, if used for a motion picture, since the persistence of an image or a mark overlaid on the moving image could annoy an audience and adversely affect the viewing experience.
The above examples for still images illustrate a key problem: an invisible watermark identifies but does not adversely affect the quality of an illegal copy, while a visible watermark can be distracting and annoying. With video and motion picture images, that include multiple images, there can be yet other problems with conventional image watermarking. For example, U.S. Pat. No. 5,960,081 (Vynne et al.) discloses applying a hidden watermark to MPEG data using motion vector data; but this method identifies and authenticates the original compressed data stream and would not provide identification for a motion picture that was copied using a camcorder. Other patents, such as U.S. Pat. No. 5,809,139 (Girod et al.), U.S. Pat. No. 6,069,914 (Cox), and U.S. Pat. No. 6,037,984 (Isnardi et al.) discuss adding an imperceptible watermark directly to the discrete cosine transform (DCT) coefficients of an MPEG-compressed video signal. These methods, however, provide a watermark that is primarily detectable in the compressed image data itself. When watermarked images are subsequently recompressed, using a lossy compression method, (with a camcorder, for example) or are modified by some other image processing operation, the watermark may no longer be detectable.
The watermarking schemes disclosed in the patents listed above add a watermark to the compressed bit stream of an image or image sequence. Alternatively, there are other watermarking schemes that add the watermark to the image data itself, rather than to the compressed data representation. An example of such a scheme is given in U.S. Pat. No. 6,044,156 (Honsinger et al.), which discloses a spread spectrum technique using a random phase carrier. However, regardless of the specific method that is used to embed a watermark, there is always a desire that a watermarking method be robust; that is, able to withstand various “attacks” meant to remove or alter the watermark. Some attacks may be deliberately aimed at the underlying structure of a given watermarking scheme and require detailed knowledge of watermarking techniques applied. However, most attack methods are less sophisticated, performing common modifications to the image such as using lossy compression, introducing low-pass filtering, or cropping the image, for example. Such modifications can be made when a video camera is used to capture a displayed motion picture. These methods present a constant threat that a watermark may be removed during the recording process.
The watermarking schemes noted above are directed to copy identification, ownership, or authentication. However, even if a watermarking approach is robust, provides copy control management, and succeeds in identifying the source of a motion picture, an invisible watermark may not be a sufficient deterrent for illegal copying.
As an alternative to watermarking, some copy deterrent schemes used in technologies other than video or movie display operate by modifying a signal or inserting a different signal to degrade the quality of illegal copies. The modified or inserted signal does not affect playback of a legally obtained manufactured copy, but adversely impacts the quality of an illegally produced copy. As an example of this principle, U.S. Pat. No. 4,644,422 (Bedini) discloses adding a degrading signal to discourage copying of audio recordings. An audio signal having a frequency at and above the high threshold frequency range for human hearing is selectively inserted into a recording. The inserted signal is not detectable to the listener. However, any unauthorized attempt to copy the recording onto tape obtains a degraded copy, since the inserted audio signal interacts adversely with the bias oscillator frequency of a tape recording head.
As a variation of the general method where a signal is inserted that does not impact viewability, but degrades copy quality, U.S. Pat. No. 6,018,374 (Wrobleski) discloses the use of a second projector in video and motion picture presentation. This second projector is used to project an infrared (IR) message onto the display screen, where the infrared message can contain, for example, a date/time stamp, theater identifying text, or other information. The infrared message is not visible to the human eye. However, because a video camera has broader spectral sensitivity that includes the IR range, the message will be clearly visible in any video camera copy made from the display screen. The same technique can be used to distort a recorded image with an “overlaid” infrared image. While the method disclosed in U.S. Pat. No. 6,018,374 can be effective for frustrating casual camcorder recording, the method has some drawbacks; including the fact that the pattern is fixed in space and, therefore, it is a relatively simple procedure to edit it from the digital data.
A more sophisticated video camera operator could minimize the effect of a projected infrared watermark by placing a filter designed to block infrared light in the video camera's optical path. A further drawback of the method is that a fourth image channel, an additional projector, or modifications to the projection screen is required to implement this method, and this additional hardware can add significant cost to a display or projection system without providing any benefit beyond defeating movie piracy.
While display systems typically provide for three color channels for the display of visible light, it is also known in the art to provide display systems which project four or more channels of visible light to enhance the viewing experience. These display systems can provide additional color primaries to expand the color gamut of the display system as described by U.S. Pat. No. 6,570,584 (Cok et al.) or to increase the brightness of the display system as described by U.S. Pat. No. 5,233,385 (Sampsell).
There remains a need for a method and a display system that allows watermarking and copy-deterrent marking of image content (e.g., motion picture content), that utilizes visible light, and yet allows the watermark information to be displayed such that it is invisible to the viewer, yet quite apparent in an illegal video copy.